The Wi-Fi (abbreviation for Wireless Fidelity), is a set of standards compatible for local networks) was created to be used in mobile devices and LANs (Local Area Network), but it is now used for Internet and wireless access VoIP (Voice over Internet Protocol). It allows a person with a computer to have an wireless connection, a PDA (personal digital assistant), o to a wireless telephone VoIP to connect to the internet when is in proximity to the access point. The geographic region covered by one or more access points are called “hotspot”.
A hotspot is any public area where computers equipped with the technology of wireless network can have access to the internet. The computer does this by contacting a wireless network using its internal NIC (Network Interface Card). The NIC searches the waves of radio generated by the wireless networks. When a strong enough signal is detected, it asks for permission to enter the. This access can be free or require registration in the network before obtaining permission to get in.
A network that generates a hotspot consist basically of a wireless router and a modem. The RF, or radio frequency, are waves utilized by a wireless network and they extend in all directions from the central location of these devices before they weaken for lack of power of the signal or interference. If a computer is inside this umbrella of RF, it will have the capacity of connecting to the network. This area is the hotspot. As the computer moves away from the routing devices and modem, the connection will become weaker and slow. The quality of the connection deteriorates quickly at the borders of this umbrella. The computer will lose completely the access if it gets out of the hotspot.
Many points of access and interfaces with the network support varying degrees of encryption to protect the traffic of interceptions. Wi-Fi is a set of global standards. Different from the cellular telephones, the same Wi-Fi client works in different countries of the world.
Problems of interoperability between brands or deviation from the standards could interrupt the connection or lower the performance of the speed in another user's devices being inside the range. The Wi-Fi Alliance establishes tests for the devices interoperability, and if the devices pass the tests are marked as Wi-Fi Certified.
The use of the bandwidth 2.4 GHz for Wi-Fi does not require a license in most countries as long as it stays below the regulatory limits and it does not interfere with other sources, including making the user device not functioning any more.
The use of frequency bandwidth is shared with applications of free-license and tolerant-to-error such as Networks of Wireless Sensors in bandwidths 868 MHz, 915 MHz and 2.450 GHz, also the Wi-Fi and cellular phones bandwidths 915 MHz, 2.450 GHz, and 5.800 GHz.
The assigning of frequency spectrum and limitations are not consistent all over the world: most European countries allow two additional channels to those in the USA for the bandwidth 2.4 GHz (1-13 vs. 1-11), while in Japan they have one more channel (1-14).
There are cases in which you want to jam intentionally the RF signal. For example in a meeting room, you may require that all the attendants be paying attention to what's happening at the meeting, and that there are no interruptions because of phone calls or reading their e-mail.
As any radio jammer, the phone jammer sends radio waves of the same frequency used by the phones. This causes enough communication interference between the cellular phone and the signal tower to make the phone unusable. In most cellular phones the network will appear simply as out of range. Most cellular phones use different bands to receive and send communications with the signal tower (it is called frequency division multiplexed or FDD). The jammers could work by means of interrupting the frequency signal from the phone to the tower or from the tower to the phone. Small hand held devices jam al bands from 800 MHz to 1900 MHz inside a range of 9 meters [Mik-09].
Is interesting the fact that it does requires less energy to interrupt the signal from the tower to the mobile phone than from the phone to the tower (also called base station), since the station is usually localized a greater distance from the jammer than the mobile phone, and it is the reason that the tower signal is not that strong.
The jammers actively emit radio signals, it may be possible that is not legal to be possessed or operated based in specific laws from the area where they are located. Examples of some countries:
Canada: illegal, except for federal agencies in charge of applying the laws and have been approved.
Popular Republic of China: used by educational departments of the government as a means to frustrate the cheating at school. During end of the year exams the phone jammers are used in all areas around high schools to prevent students inside receiving calls or messages that can be used for illegal purposes. In some municipalities instead of using jammers, the signal towers close to the school are temporary closed for the duration of the week of exams.
Mexico: legal inside jails, only used in churches and hospitals.
United Kingdom: illegal to use, but legal to have. Installing inside jails has been proposed.
United States of America: jammers of phones are used by federal agents under certain circumstances. The privacy rights of the owners could affect the policy and use inside buildings. The Federal Communication Commission FCC) can give a permission to overrule the laws of private use. For radio communications it is illegal to operate, manufacture or offer for sale including announcements.
Today there are many jammers of wireless signals, mainly for cellular phones [Hua-09], [Bre-06], [New-91] [Lee-93]. As far as Wi-Fi jamming, most of the devices that exist are to monitor the existence of interference with a PC [Wiki1-09]. You can find a list of products for jamming Wi-Fi in [Jam-11]. There are a great variety of jammers when the user of the mobile device is in a car [Cat-11], [Bro-11], [Nat-10], [Mar-04], and general signal jammers [Hig-10], [Jos-10], [STO-10] [Are-11].
All the jammers of wireless signals before mentioned have in common that there is no delimiting of the geographical location where the jamming is done. This jamming is delimited only by the power of the generated signal. There are many cases which it is desired to jam a specific area, for example you may want to jam a meeting room, a movie theatre, a classroom where a professor is teaching, a church, etc., and you don't want to interfere with other close areas or nearby spaces to the area you want to jam. For example a professor may not want his students to have access to internet inside the classroom so that the students do not distract themselves, but the professor in the adjacent classroom needs for his students to have access to the internet in his classroom. A company requires that all persons in assistance to a meeting room do not have access to their cell phones or internet, and avoid interruptions, but any other area outside of this meeting room must have all the wireless signal services of cellular phones and internet.
The present patent provides a solution to the problem of how to restrict the wireless signal in a specific geographic area. In order to generate jamming signals in a delimited geographical area this patent obtains and calculates in which direction and at which power the emitter of jamming signal should send its jamming signals. This jamming signal will make all the devices that are inside the geographical area and are using the signal that is being jammed unable to receive correctly (unusable) the wireless signal. Examples of these wireless signals that could be jammed are the signals for cellular phones and internet signals. This patent will cover an important part of today's commercial market needing protection like schools, universities, companies, churches and movie theaters among others. Civil protection and the military are also markets in need of our patent.